Cigna Corp. became the third national health insurer to reach an agreement with New York's attorney general over how it determines payments for out-of-network medical care provided to its plan participants. Under the agreement, Cigna will contribute $10 million to a new, independent database that it and other insurers plan to use to calculate how much they should pay for doctors and hospitals outside of their networks. The pact comes on the heels of similar deals with UnitedHealth Group Inc., Aetna Inc. and several smaller New-York based insurers.